The present invention relates to cylinder locks, and particularly to a device and method for its use for determining the required profile for a key for such a lock, without first unlocking the lock.
Cylinder locks are of several types such as those including pin tumblers and those including wafer tumblers which must be pushed into the proper positions by inserting a key into a keyhole in the cylinder of the lock in order for the cylinder of the lock to be turned relative to the outer casing. When the proper key is used the pin tumblers or wafer tumblers are moved to a position in which each tumbler is located within the volume defined generally by the outer surface of the cylinder of the lock. If the profile of the key is not correct, however, one or more of the tumblers extends from the inner cylinder into an appropriate groove in the surrounding casing, preventing the cylinder from being turned relative to the casing.
When the key from a lock has been lost a new key can be made by disassembling the lock to determine the proper profile, but this is often a very expensive procedure, because of the amount of time required to remove the lock from, for example, a door of an automobile. It is therefore desired to construct a new key without having to disassemble the lock.
As shown in Rubens U.S. Pat. No. 3,087,050 it is known that cylinder locks having wafer tumblers can be decoded to permit a new key to be cut, without unlocking the lock, by visually observing the positions of the individual wafers with the aid of a lamp and a probe which is used to hold some of the tumbler wafers out of the line of sight while observing others. This method of decoding a lock requires accurate estimation of the position of each tumbler within the lock, which may be difficult, because of the small differences in locations of tumbler positions, or because of reflections of light within the lock.
Hansen U.S. Pat. No. 1,991,151 shows a device used for decoding cylinder locks, but the device shown by Hansen appears to be somewhat complex and to be somewhat slow to use. Other devices, such as those shown in Harwell U.S. Pat. Nos. 2,720,032 and 2,791,840, and in Abrams U.S. Pat. No. 2,087,423, Tampke U.S. Pat. No. 2,727,312, and Nail U.S. Pat. No. 4,185,482 require that a lock first be opened before those devices can be used to determine the correct profile of a key for the lock. That is, the tumblers must all be moved to the position in which the break line of each tumbler corresponds with the surface between the inner and outer cylinders of the lock.
Johnstone U.S. Pat. No. 2,338,768, and Jarm U.S. Pat. No. 4,186,577 show devices which aid in picking cylinder locks. Johnstone discloses a set of partial keys by which a lock can be opened by systematically trying different parts along a key shank to bring each tumbler into a position coinciding with the break line between the cylinder and the surrounding casing. European patent application 82303966.4 discloses a device for picking a lock, in which a device is used to raise all of the tumblers to a non-interfering position to permit insertion into the keyway of a device which can be used to make an impression of the tumblers as they are allowed to move into an unlocked position.
Easley U.S. Pat. No. 4,517,746 discloses a lock decoding device including a probe including stiff wires which are rotatable within the probe to determine the positions and types of individual wafers of a certain type of cylinder lock without opening the lock. What is needed, however, is a simpler device, for use with wafer-type cylinder locks, to determine the proper profile for a key for such a lock without first having to pick the lock.
Ordinarily, the wafers of a wafer-type cylinder lock are interchangeable to make the lock use a different key. Each wafer is cut to one of several different sets of dimensions corresponding to a notch of a particular depth, to be located at a point along the shank of a key for such a lock which corresponds with the position in which that particular wafer tumbler is located within the cylinder of the lock. Any one of two to five or more different wafers might be in any particular wafer position of the cylinder, and what is needed is a device to determine which wafer is in each position of the cylinder of the lock, without first having to pick and open the lock. In wafer-type cylinder locks of the type for which a preferred embodiment of the present invention is intended, a hole is provided centrally in each wafer, permitting the wafer to move within the cylinder when a key is inserted into the keyhole. The position of the hole relative to the ends of the wafer determines the required depth of the notch on the working surface of a key, for each wafer position of the cylinder of the lock.